// --------------------------------------------------------------------------------------------------------------------
// <copyright company="" file="StreamManipulator.cs">
//   
// </copyright>
// <summary>
//   (c) Copyright Ascensio System Limited 2008-2009
// </summary>
// --------------------------------------------------------------------------------------------------------------------

namespace agsXMPP.IO.Compression.Streams
{
    #region usings

    using System;

    #endregion

    /// <summary>
    /// This class allows us to retrieve a specified number of bits from
    /// the input buffer, as well as copy big byte blocks.
    /// 
    /// It uses an int buffer to store up to 31 bits for direct
    /// manipulation.  This guarantees that we can get at least 16 bits,
    /// but we only need at most 15, so this is all safe.
    /// 
    /// There are some optimizations in this class, for example, you must
    /// never peek more than 8 bits more than needed, and you must first
    /// peek bits before you may drop them.  This is not a general purpose
    /// class but optimized for the behaviour of the Inflater.
    /// 
    /// authors of the original java version : John Leuner, Jochen Hoenicke
    /// </summary>
    public class StreamManipulator
    {
        #region Members

        /// <summary>
        /// </summary>
        private int bits_in_buffer;

        /// <summary>
        /// </summary>
        private uint buffer;

        /// <summary>
        /// </summary>
        private byte[] window;

        /// <summary>
        /// </summary>
        private int window_end;

        /// <summary>
        /// </summary>
        private int window_start;

        #endregion

        #region Properties

        /// <summary>
        /// Gets the number of bits available in the bit buffer.  This must be
        /// only called when a previous PeekBits() returned -1.
        /// </summary>
        /// <returns>
        /// the number of bits available.
        /// </returns>
        public int AvailableBits
        {
            get { return bits_in_buffer; }
        }

        /// <summary>
        /// Gets the number of bytes available.
        /// </summary>
        /// <returns>
        /// The number of bytes available.
        /// </returns>
        public int AvailableBytes
        {
            get { return window_end - window_start + (bits_in_buffer >> 3); }
        }

        /// <summary>
        /// Returns true when SetInput can be called
        /// </summary>
        public bool IsNeedingInput
        {
            get { return window_start == window_end; }
        }

        #endregion

        #region Methods

        /// <summary>
        /// Get the next n bits but don't increase input pointer.  n must be
        /// less or equal 16 and if this call succeeds, you must drop
        /// at least n - 8 bits in the next call.
        /// </summary>
        /// <param name="n">
        /// </param>
        /// <returns>
        /// the value of the bits, or -1 if not enough bits available.  */
        /// </returns>
        public int PeekBits(int n)
        {
            if (bits_in_buffer < n)
            {
                if (window_start == window_end)
                {
                    return -1; // ok
                }

                buffer |=
                    (uint)
                    ((window[window_start++] & 0xff | (window[window_start++] & 0xff) << 8) << bits_in_buffer);
                bits_in_buffer += 16;
            }

            return (int) (buffer & ((1 << n) - 1));
        }

        /// <summary>
        /// Drops the next n bits from the input.  You should have called PeekBits
        /// with a bigger or equal n before, to make sure that enough bits are in
        /// the bit buffer.
        /// </summary>
        /// <param name="n">
        /// </param>
        public void DropBits(int n)
        {
            buffer >>= n;
            bits_in_buffer -= n;
        }

        /// <summary>
        /// Gets the next n bits and increases input pointer.  This is equivalent
        /// to PeekBits followed by dropBits, except for correct error handling.
        /// </summary>
        /// <param name="n">
        /// </param>
        /// <returns>
        /// the value of the bits, or -1 if not enough bits available.
        /// </returns>
        public int GetBits(int n)
        {
            int bits = PeekBits(n);
            if (bits >= 0)
            {
                DropBits(n);
            }

            return bits;
        }

        /// <summary>
        /// Skips to the next byte boundary.
        /// </summary>
        public void SkipToByteBoundary()
        {
            buffer >>= bits_in_buffer & 7;
            bits_in_buffer &= ~7;
        }

        /// <summary>
        /// Copies length bytes from input buffer to output buffer starting
        /// at output[offset].  You have to make sure, that the buffer is
        /// byte aligned.  If not enough bytes are available, copies fewer
        /// bytes.
        /// </summary>
        /// <param name="output">
        /// The buffer to copy bytes to.
        /// </param>
        /// <param name="offset">
        /// The offset in the buffer at which copying starts
        /// </param>
        /// <param name="length">
        /// The length to copy, 0 is allowed.
        /// </param>
        /// <returns>
        /// The number of bytes copied, 0 if no bytes were available.
        /// </returns>
        /// <exception cref="ArgumentOutOfRangeException">
        /// Length is less than zero
        /// </exception>
        /// <exception cref="InvalidOperationException">
        /// Bit buffer isnt byte aligned
        /// </exception>
        public int CopyBytes(byte[] output, int offset, int length)
        {
            if (length < 0)
            {
                throw new ArgumentOutOfRangeException("length");
            }

            if ((bits_in_buffer & 7) != 0)
            {
                /* bits_in_buffer may only be 0 or a multiple of 8 */
                throw new InvalidOperationException("Bit buffer is not byte aligned!");
            }

            int count = 0;
            while (bits_in_buffer > 0 && length > 0)
            {
                output[offset++] = (byte) buffer;
                buffer >>= 8;
                bits_in_buffer -= 8;
                length--;
                count++;
            }

            if (length == 0)
            {
                return count;
            }

            int avail = window_end - window_start;
            if (length > avail)
            {
                length = avail;
            }

            Array.Copy(window, window_start, output, offset, length);
            window_start += length;

            if (((window_start - window_end) & 1) != 0)
            {
                /* We always want an even number of bytes in input, see peekBits */
                buffer = (uint) (window[window_start++] & 0xff);
                bits_in_buffer = 8;
            }

            return count + length;
        }

        /// <summary>
        /// resets state and empties internal buffers
        /// </summary>
        public void Reset()
        {
            buffer = (uint) (window_start = window_end = bits_in_buffer = 0);
        }

        /// <summary>
        /// Add more input for consumption.
        /// Only call when IsNeedingInput returns true
        /// </summary>
        /// <param name="buf">
        /// data to be input
        /// </param>
        /// <param name="off">
        /// offset of first byte of input
        /// </param>
        /// <param name="len">
        /// length of input
        /// </param>
        public void SetInput(byte[] buf, int off, int len)
        {
            if (window_start < window_end)
            {
                throw new InvalidOperationException("Old input was not completely processed");
            }

            int end = off + len;

            /* We want to throw an ArrayIndexOutOfBoundsException early.  The
			* check is very tricky: it also handles integer wrap around.
			*/
            if (0 > off || off > end || end > buf.Length)
            {
                throw new ArgumentOutOfRangeException();
            }

            if ((len & 1) != 0)
            {
                /* We always want an even number of bytes in input, see peekBits */
                buffer |= (uint) ((buf[off++] & 0xff) << bits_in_buffer);
                bits_in_buffer += 8;
            }

            window = buf;
            window_start = off;
            window_end = end;
        }

        #endregion
    }
}